Previous studies reported that about 20% of patients with IgAN had decreased sC3 levels at kidney biopsy [23,28], similarly to our findings; in a retrospective study [14], patients with decreased sC3 levels had more intense deposition of C3 in the mesangium than those who had normal sC3 levels, and serum C3 levels were significantly associated with progression to kidney failure. The gene discussed is C3; the disease is kidney failure.